This invention relates to thermonuclear fusion reactors and specifically to a method and system for producing and maintaining a thick flowing liquid lithium blanket or first wall for toroidal magnetic confinement deuterium-tritium (DT) fusion reactors.
Prior art conceptual designs of toroidal magnetic confinement DT fusion reactors included an extremely complicated xe2x80x9cblanketxe2x80x9d located adjacent to and surrounding the fusion plasma. In many designs, the blanket is composed of solid materials which act as a plasma facing xe2x80x9cfirst wallxe2x80x9d and as plumbing to carry a heat transfer fluid which functions to transfer the heat generated by the fusion plasma from the reactor to an external heat sink. It is expected that these solid material blankets would be severely damaged over time by the bombardment of high energy fusion neutrons, by erosion caused by sputtering, by high heat fluxes during normal operations, and by very high heat fluxes, ablation, and large electromagnetic forces during plasma disruptions.
In a field which is not yet developed, such as fusion reactors, design parameters are difficult to quantify. Technical studies have identified the prior art blanket as a problem area, one which some critics have insisted threatens the economic practicality of fusion power. Anticipated initial development costs of the prior art blankets was dominated by the need to synthesize new solid materials capable of operating in the severe environment of a fusion reactor with a focus on reducing the unavoidable periodic replacement of the blanket components. Anticipated recurring costs included frequent replacement and repair of the components by complex new modules made of the hypothetical new materials. The projected overall fusion economics was also governed by the need to design for heat fluxes in blanket components.
Applicant""s liquid metal blanket system and method provides for flowing a thick liquid lithium blanket or first wall adjacent to the plasma. Since liquid lithium has no crystalline structure, it can not be damaged by high energy fusion neutron bombardment. The layer of liquid lithium also protects solid objects under the layer by acting as a moderator to slow the fusion neutrons to benign energy levels after they pass through the lithium layer. Since the first wall or lithium layer is in motion, it is continually renewing itself and thus, will not be permanently damaged by sputtering erosion, ablation, or the presence of mechanical cracks as are solid structures. In addition, due to the large thermal capacity of liquid lithium, the flowing lithium layer can provide for high heat flux rates. In another embodiment, the insulators and electrodes, present in the apparatus, have a distorted shape or orientation to minimize neutron streaming. A further embodiment employs the use of an insulator positioned at the top of the toroid, containing the plasma, and one positioned at the bottom, thus, separating the lithium streams both at the top and bottom of the toroid. This improves the distribution of the electrical potential facing the plasma. In the final embodiment, two liquid lithium layers are nested to form a low vapor pressure surface.
Accordingly a first object of the present invention is to provide a first wall which does not incur significant damage under bombardment by high energy neutrons.
A second object of the invention is to provide a moving layer with good thermal properties to provide high heat flux densities to remove the heat generated by the fusion process.
A third object of the invention is to provide a method and system for producing and maintaining a thick flowing first wall.
Other objects and advantages of the invention will become apparent from the following description and accompanying drawings.
The subject invention is a flowing liquid metal, preferably lithium, first wall or blanket for a toroidal magnetic confinement deuterium-tritium (DT) fusion reactor. The presence of a flowing layer or blanket adjacent to the plasma to form a first wall eliminates neutron damage. In addition since liquid lithium is a good conductor of heat, the flowing liquid layer allows for the use of high heat flux densities.
The first wall is formed by injecting two axisymmetric positioned streams of liquid metal, preferably lithium, through an entry port at the top portion of a toroidal chamber containing the fusion plasma. An electrical current is supplied to both streams of liquid lithium in such a manner that the direction of current flow in the liquid lithium layer is the same as the direction of current flow in the toroidal field coils. The force on the lithium layer due to the current flowing in the lithium in combination with the magnetic field internal to the toroid keeps the lithium layer in contact with the inner wall of the toroid. On reaching the bottom of the toroidal chamber both lithium streams flow out of the chamber and are reprocessed to be used again. Modifications to the positioning of the current electrodes and insulators can be made to change the properties of the system.
In an alternate embodiment, the liquid lithium layer is composed of two sublayers of liquid lithium each at a different temperature. The outer sublayer next to the toroid wall is warmer than the inner sublayer which is next to the plasma. the inner sublayer is heated by the fusion plasma during its descent and on reaching the base of the toroid the liquid lithium exits the toroid and is pumped back to the top of the toroid to be injected as the outer sublayer. This embodiment serves to reduce the vapor pressure of the inner liquid lithium sublayer.